Refining pressure tar



Filed July 5, 1932 m 6 WW M MD ATTORNEY Patented Oct. 26, 1937 REFINING PRESSURE TAR Robert E. Wilson, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application July 5, 1932, Serial 'No. 620,838 3 Claims. (01. 196-13) This invention relates to a process of refinin pressure tar and more particularly to a method and means for utilizing the pressure tar from cracking operations.

In the production of cracked gasoline, mineral oils of various types are heated to about 750 to 1000 F., at pressures'of about 100 to 1000 pounds per square inch, and the reaction products are maintained under pressure at elevated temperatures for a sufficient period to convert the oils into light hydrocarbons, such as gasoline and heavy hydrocarbons, which are generally called pressure tar. The utilization of pressure tar is a problem which has confronted petroleum refiners since the beginning of the cracking industry. This tar has heretofore been used as a cheap fuel or road surfacing material, and much of this oil has not been entirely satisfactory even for these uses.

The object of my invention is to provide a means for converting this type of material into more valuable products; particularly to recover clean oil of high heating value for use as a fuel or for use as a cracking or hydrogenation stock.

- A further object is to prepare from this tar an improved road oil characterized by a high hexane insoluble content. Other objects will be apparent from the following detailed description. 7

In practicing my invention I separate the tar into two fractions each of which is more valuable than the original material. I treat the tar with a solvent for separating the asphalt from paraflinic and naphthenic oils, preferably using a liquefied normally gaseous light hydrocarbon, such as propane. I have found that propane will precipitate about half of the reduced pressure tar as asphalt. The remaining half is anioily liquid of red or brown color closely resembling lubricating oils of intermediate viscositylabout 300 seconds Saybolt at 100 F.) and having a high density (about 12 A. P. 1.), a hig'hj vapor pressure and a low boiling point. 0 3 liquid is. suitable for lubricating purposes-where high volatilityis desired, as with Diesel engines. It is particularly valuable as a charglng stock for cracking and hydrogenation processeswhere it yields a motor fuel of unusually high knock-rating characteristics. Gasoline prepared from this stock will have a knock-rating of '75 octane number or higher, and may be marketed as a premium motor fuel.

The asphalt which is precipitated by the propane is characterized by a very highhexane insoluble content and it may be blended with road oils to increase their hexane insoluble content and to improve their characteristics generally. The precipitation of asphalt from pressure tar by propane gives a product which, in many re-' ,spects, resembles high melting asphalt and it stood that it is equally applicable to tars from vapor phase processes operating at low pressures. In my preferred example I will describe a pressure tar from a Holmes-Manley cracking unit operated at, about 900 F. undera pressure of about 300. pounds per square inch.

The pressure tar from this cracking unit is flashed (distilled by its contained heat) at atmospheric pressure to yield a reduced pressure tar having a furol viscosity at 122 F. of about 125. This tar has a hexane insoluble content of.

only about 8% to 10%.

This reduced pressure tar at about 400 to 500 F. is introduced into the system through line, [0, .30 passed through coil H in asphalt still l2, and

thence through cooler 13 to mixer M wherein it is thoroughly mixed with propane from storage tank I5, pipe 16, pump 11 and pipe l8 or used propane from pipe 19. The mixture is preferably 5 Ma temperature of about 150 to 100 F., and I may use about four or five volumes of propane per volume of pressure tar. If desired, 1 may conduct the separation with propane at still lower temperatures, for example I may operate at a temperature of-about to F. It should be understood that impure propane, ethane, isobutane, butane, etc., and/or mixturesthereof, may be used in the place of pure propane. Also the proportionsof propane to pressure tar may 45 be varied through a relatively wide range depending upon the degree of separation required, the amount of. oil to be removed from the pressure tar, the type of apparatus used, etc. 1

The mixture of pressure tar and propane, preferably at about to 100 F. is introduced through pipe 20 and valve 2| into settling chamber '22, the temperature of which may be controlled by the vaporization of a part'of the propane, vapors being removed through pipe 2:

and compressor 24, or by-pass 25 to condenser 26 and storage tank I5. The asphalt precipitates rapidly even at high temperatures and may be withdrawn from the bottom of the settler through conduit 21 by conveyor 28 and introduced into the asphalt still l2 wherein propane is removed. Instead-of settling, I may filter the precipitated asphalt, especially when large amounts of propane are used. The finished asphalt is withdrawn through pipe 29 to storage tank 30 and the propane is conducted under high pressure through pipe 3| to condenser 32. wherein it is liquefied and returned to storage tank I5.

The upper liquid layer in the settling chamber 22 consists of propane and dissolved oil and it may be transferred fromsettling chamber 22 through pipe 33, pump 34, and pipe i9 back to the inlet of the mixer; when a relatively small amount of oil is to be removed from the pressure tar, the propane may thus be recycled for a considerable length of time. However, in my preferred embodiment I withdraw the propane solution through pipes 36 and 31 to tower 38, which is heated by steam or hot water in coil 39, separated oil being withdrawn through pipe 40 and propane vapors being returned through pipe 4| to condenser 42 and propane storage tank l5. Alternatively the propane may be removed by flashing under reduced pressure. The oil which is removed through pipe 40 is substantially asphalt free, it is clean, it has an exceptionally high heat content, and it makes an excellent burning oil. Furthermore, it may, if desired, be used as a charging stock for making further amounts of cracked gasoline or as a hydrogenation stock.

In some instances it may be desired to separate wax or other impurities which might be present in an asphaltic residuum and which might not be separated in settling chamber 22 at high temperatures. In such cases I pass the propane solution from the top of settling chamber 22 through reducing valve 43 to a second settling chamber 44 which is cooled by external means and/or maintained at low temperature by the removal of propane gases through pipe 45 and pump 46 or by-pass 41 to condenser 26 and storage tank l5. In settling chamber 44 I may obtain temperatures as low as 30 F., 50 F., or at even lower temperatures when hydrocarbons lower than propane alone are used. At this temperature I may separate a considerable amount of waxy or asphaltic substances which were not removed in settling chamber 22. The precipitated substances may be withdrawn through conveyor 48 to boiler 49 wherein the propane is removed by heater 50 and conducted by pipe 5| back to a suitable condenser and to storage tank 15. The finished material, which will be an asphalt of a different character from that obtained in stripper I2, may be withdrawn through pipe 52 and stored in tank 53. The propane solution from the second chiller may be transferred by pipe 54 to boiler 38 and the propane may be removed therefrom as hereinabove described.

If additional propane is required for the chilling operations or forwashing or further dilution, it may be supplied to either settling chamber 22 or 44 directly from storage tank l5 through pipes 55 and 56 or 51. either batchwise or continuously, and when it is operated batchwise the propane solution may be transferred by pipe-58 to reboiler 38 after the asphalt has been removed from the settling chamber.

The system may be operated It will be obvious, of course, that all of the above equipment must be designed, to withstand high pressures and should preferably be well insulated. Various connections, operating valves, safety valves, etc. may be used in accordance with ordinary engineering practice. Other washing steps, countercurrent extraction steps and asphalt separation under widely varying temperature conditions are contemplated. In some cases it may be necessary or advisable to melt or dissolve the precipitated asphalt to facilitate its transfer from one part of the system to another,one skilled in the art will use heaters where necessary, steam jacketed pipes, etc., or he will add diluents or solvents as the occasion may demand.

I have found that the recovered asphalt has new and valuable properties and that it may be used in many new fields, particularly in the fields of roofing material, insulation, weather proofing, etc. I have also found that the asphalt from storage tank 30 may be blended in small amounts with road oils to markedly increase their hexane insoluble content, and to otherwise improve their character. The method of determining the hexane insoluble content of a road oil is described as Test 23 in Abraham Asphalts and AlliedSubstances (Van Nostrand 1929, page 724). I have found that the asphalt precipitated from pressure tar, as hereinabove described, may contain upwards of 30% hexane insoluble matted-appreciably greater amounts of hexane insoluble substances than contained in the original pressure tar. It appears, therefore, that the hexane insoluble substances are not merely concentrated but are even increased. The blending of this asphalt with reduced pressure tar yields an excellent road oil.

While I have described the use of propane as a normally gaseous diluent, it should be understood that any solvent may be used which has the property of separating the components of the pressure tar as hereinabove described. A normally gaseous light hydrocarbon, such as propane, ethane, butane, ethylene, etc. is particularly useful for this purpose, but substituted hydrocarbons or other organic solvents having high precipitating power for these asphaltic materials may likewise be used.

I have described in detail a preferred embodi- .ment of my invention, but it should be undertemperature of about to F. and under a pressure suflicient to maintain said hydrocarbons in liquid phase, separating the resulting mixture into a portion soluble in said hydrocarbons and a portion insoluble in said hydrocarbons, recovering said insoluble portion and blending it with a blending oil derived from pressure tar to produce an improved road oil having a higher content of material insoluble in hexane than that of the original pressure tar or said blending oil.

2. The method in accordance with claim wherein the normally gaseous hydrocarbon is propane.

into a portion soluble in said hydrocarbons and a portion insoluble in said hydrocarbons, recovering said insoluble portion and blending it with a. blending oil derived from pressure tar to produce an improved road oil having a higher content of material insoluble in hexane'than that of the original pressure tar or said blending oil.

ROBERT E. WILSON. 

